1. Technical Field of the Invention
This invention most generally relates to switches for RF signals and applications, and more particularly to RF electromechanical single pole single throw (SPST) switches.
2. Background Art
Mechanical switches are well known in the industry as being reliable and dependable. Such devices were the backbone of the industry for controlling telecommunication signals and RF and microwave signals. The mechanical switches in the past lasted only a few million cycles with few failures and most were not successfully used in extreme environments.
Despite their success, the switches were somewhat expensive, difficult to manufacture and occupied considerable space in many compact electrical designs. As semiconductor technology developed, transistorized switches replaced electromechanical switches in many RF systems. However, if a fail safe mode is required, electromechanical switches are superior, as they are more rugged and can provide optimal switching characteristics. In the higher end of the frequency spectrum mechanical switches are more convenient and flexible for adjustment to matching and broadband performance.
One of the concerns with modem electronic applications is space. Modem devices require compact components, and switches must be able to fit within the allotted space. Another factor for switches is to provide a low loss path when the switch is xe2x80x9cONxe2x80x9d and a high loss path when the switch is xe2x80x9cOFFxe2x80x9d. And, when the switch is xe2x80x9cOFFxe2x80x9d there should be negligible interference, such as an increased inductance in the circuit.
The prior art has attempted to solve the deficiencies noted. The existing standard fast switching elements are reed switches. Reed switches are used in a variety of devices, for example, in the coaxial reverse power protection relay in U.S. Pat. No. 5,258,731 (""731). In the reed relay the reed switch is enclosed within the central channel of the conductive body. Within the channel, the reed switch is concentrically surrounded by a conductive elastomeric tube, and a magnetic coil is wound around a portion of the body. When energized, the coil produces a magnetic field that closes the reed switch. When de-energized, the coil""s magnetic field ceases, opening the reed switch. The reed switch, along with the center contacts, form a center conductor within the channel of the relay body. The body and elastomeric tube form an outer conductor. The relay is impedance matched to RF connectors and system transmission line impedances. A nonuniform impedance occurring along the length of the reed switch is balanced by the conforming tube walls. However, this single pole single throw device has no termination of the contacts and the ""731 patent relies upon the tube body to perform as a conformal ground.
Another device, U.S. Pat. No. 4,870,385 is a coaxial relay switch having an electrically conductive resin injected into the switch space that rigidly mounts the internal workings. The resin is used to provide some degree of shielding of the signals, and once again, there is no termination.
While being miniature and fast, reed relays cannot be used for switching RF signals because the reed relays do not terminate the system when open, so the reed switch is inadequate in the capacitance portion of the reactance parameter to provide a good match for optimal broadband performance (the return loss has to be within xe2x88x9215 dB). The matching within the device can be done by means of reshaping the tube and the central channel requiring customization and additional complexity, time, and cost.
Accordingly, what is needed is a switch structure that can terminate an RF system when open to provide the return loss within xe2x88x9215 dB in broadband applications, and to be easily matched over the whole frequency range. As a matter of course, the switch needs to be a reliable and dependable device in the RF range up to 3 GHz, incorporating the switching speed and hermetic seal of the reed switch. Such a device also needs to be very compact and, at the same time, rugged and able to take some physical and environmental stress.
The essence of the present invention is a miniature mechanical switch that addresses the aforementioned problems. In a preferred embodiment the present invention is an RF electromechanical single pole single throw (SPST) switch. More particularly, the present invention is a compact hermetically sealed switch providing a low loss path for RF signals in closed position and a high impedance path for RF signals in open position. As compared to state-of-the art electromechanical devices, the present switch is ten times smaller and forty times faster with a frequency range from DC xe2x88x923 GHz, switching time 1 ms minimum, repetition frequency 2 KHz minimum, and a life expectancy of not less than 100 million cycles.
The present invention is a structure with adequate capacitance in broadband applications, easily matched, has RF terminations when open, and essentially preserves all the advantages of the reed switch.
The structure according to the present invention includes two reed switches each having an actuator and two contacts. The actuator is normally contacted with one of the contacts. Both reed switches are electrically connected in parallel and mechanically attached to each other in a way where their actuators go to contacts in opposite direction if switching. One identical contact in each reed switch is grounded, and the actuator and another contact are connected to RF path in series. The actuators are connected together and to a connector pin on the RF input end of the switch. One pair of the identical contacts are connected together and to another connector pin on the RF output end of the switch. Another pair of the identical contacts are connected to the shell of the connector on the output end of the switch. Which pair connected to the pin and which one to the shell depends on what kind of switch is needed: normally open or normally closed.
On the input end of the switch the connector""s pin is elongated and surrounded by a matching sleeve. In the preferred embodiment of the invention there is a male SMA connector on the input end and a female SMA connector on the output end. The male connector is concentrically attached to the non-ferrous tube having several portions each with different diameter and wall thickness. The reed switches are concentrically disposed in the tube. The female connector is also concentrically attached to the end of the tube oppositely to the male connector. On the outside of the tube a coil is disposed having DC input and output.
Thus, the structure according to the present invention is a very simple mechanically rugged unit. This unit can be matched in easy way, without any changes in shape its machined or formed portions. The two reed switches connected in parallel add to the capacitance portion of the impedance caused the expanded RF performance range of the switch. The matching can be achieved by changing the material of the sleeve and/or its length. The normal state of the switch (whether normally open or close) can be achieved by turning each reed switch at 180 degrees about their longitudinal axes.
It is an object of the present invention to have mechanically sound, simple, reliable and inexpensive switch. And, a further object of the invention is the sizexe2x80x94the performance and characteristics achieved by the device are in a package that fits within most electrical applications.
It is a further object of the present invention to have a switch that can be easily changed from normally close to normally open state.
It is another object of the present invention to have a switch that can perform in the RF frequency range from DC to 3 GHz with a switching time better than 1 ms, repetition frequency better than 2 KHz, and life span more than 100M cycles.
An object of the invention is an electromechanical RF switch, comprising a housing having an input end and an output end with a biasing means for actuating the switch. There are a pair of reed relays within the housing, each relay having a switchable actuator with a first contact and a second contact connectable to said switchable actuator, wherein each switchable actuator is electrically connected and wherein each first contact is connected to a grounded shell and each second contact is electrically connected together. An input connecter is connectable to the input end having an input pin electrically connected to the switchable actuator, and an output connector connectable to the output end having an output pin electrically connected to the second contact.
Additionally, an object includes the electromechanical RF switch, further comprising a sleeve having RF absorbing properties surrounding the input pin. And, further comprising a means for matching an RF path, wherein the sleeve is made from a material having a dielectric constant that alters an impedance of the RF path, and the matching means is selecting the material for a particular frequency. Furthermore, a means for matching the RF path, wherein a length of the sleeve alters an impedance of the RF path and the matching means is performed by adjusting the sleeve length for a particular frequency.
Another object is the electromechanical RF switch, wherein each reed relay is hermetically sealed in a glass tube. In addition, wherein the input pin is removable.
An object also includes the electromechanical RF switch, wherein the switch is normally closed with each actuator electrically connected to each second contact. In addition, wherein the switch is changeable from normally closed to normally open by rotating each reed relay 180 degrees so that each first contact is then connected to each actuator and each second contact is then connected to thewgrounded shell.
And an additional object, wherein the biasing means is a coil with a DC input and a DC output. And, wherein the input and output connectors are SMA.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the detailed description, wherein we have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by us on carrying out our invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.